The present invention relates to a polybenzoxazole precursor and a production process for the same. Also, the present invention relates to a coating composition capable of forming a film which is excellent in an electrical insulating property, a heat resistance and a mechanical strength and which is useful particularly as a protective film or an insulating film for a semiconductor element or a circuit board such as a printed board.
Further, the present invention relates to a positive type light-sensitive resin composition suited as a resist which is excellent in an operation stability and highly reliable for forming a conductor image, particularly an etching resist for producing a printed wiring board and to a method for forming a pattern using the same resin composition.
A polyimide resin which is excellent in thermal and mechanical characteristics has so far been used as a film organic material for protecting and insulating a semiconductor element or a circuit board such as a printed board.
Further, in recent years, a light-sensitive polyimide resin which is excellent in a heat resistance and mechanical characteristics is being used as an organic material for the purpose of forming a circuit pattern on a semiconductor element or an electronic or electric circuit board such as a printed board and protecting and insulating it. In such light-sensitive polyimide resin composition, negative type ones in which an exposed part is cured and insolubilized are disclosed in many documents including Japanese Patent Publication No. 030207/1980 (=DE-A-2437413) and Japanese Patent Application Laid-Open No. 145794/1979 (=U.S. Pat. No. 4,243,743). However, negative type light-sensitive polyimide resin compositions have problems on a sensitivity, a resolution and a processability, and positive type light-sensitive polyimide resin compositions are disclosed in Japanese Patent Application Laid-Open No. 324493/1994, Japanese Patent Application Laid-Open No. 179604/1995 and Japanese Patent Application Laid-Open No. 143980/2000 for the purpose of improving them.
In general, however, polyimide resins are highly hygroscopic and have a problem in terms of electrical characteristics. Particularly in recent years, fined circuits and accelerated signals make it impossible for them to sufficiently meet required electrical characteristics.
On the other hand, a polybenzoxazole resin is excellent in an electric insulating property as well as a heat resistance and a mechanical strength and therefore is expected as sufficiently applicable to uses in which electronic equipments proceeds to a higher density and a higher performance in the future. A film of the polybenzoxazole resin has a high heat resistance, excellent electrical characteristics and fine processability, and therefore investigated is availability thereof not only for wafer coating but also as an interlayer insulating resin.
For example, positive type light-sensitive resins constituted from polybenzoxazole precursors and diazoquinone compounds are disclosed in Japanese Patent Publication No. 46862/1999 (=U.S. Pat. No. 4,339,521) and Japanese Patent Application Laid-Open No. 281441/1995. The polybenzoxazole precursors used for them are usually produced by reacting dicarboxylic chloride with suitable bis-o-aminophenol (EP-A-0264678 and EP-A-0291779). However, hydrogen chloride (HCl) is produced in these reactions, and therefore soluble bases such as pyridine and ethylamine have to be usually added in order to scavenge it. If chlorides formed from them remain in the product, they are likely to exert an adverse effect on a semiconductor element and an electronic or electric circuit, so that they have to be completely removed by, for example, ion exchangers. However, it is difficult to obtain a polybenzoxazole precursor having a high purity by the method described above, and labor is required for refining it and allows the cost to go up.
Then, disclosed in Japanese Patent Application Laid-Open No. 183846/1997 (=EP-A-761718, U.S. Pat. No. 5,807,969) is a process for producing a polybenzoxazole precursor via a dicarboxylic acid derivative obtained by reacting 1-hydroxybenzotriazole with dicarboxylic acid. However, carbodiimide has to be usually used as a condensing agent for producing the above dicarboxylic acid derivative, and a urea compound is produced as a by-product. Accordingly, a refining step for removing this urea compound is required as well in this process, and a polybenzoxazole precursor having a high purity can not readily be obtained.
An object of the present invention is to provide a novel polybenzoxazole precursor having a high purity which does not contain ionic by-products exerting an adverse effect on the electric characteristics.
Another object of the present invention is to provide a production process for such polybenzoxazole precursor.
A different object of the present invention is to provide a coating composition capable of forming a film which is excellent in an electrical insulating property, a heat resistance and a mechanical strength and which is useful particularly as a protective film or an insulating film for a semiconductor element or a circuit board such as a printed board.
A further different object of the present invention is to provide a positive type light-sensitive resin composition which does not contain impurities such as chlorides exerting an adverse effect on a semiconductor element and an electronic or electric circuit and is inexpensive and excellent in a heat resistance, mechanical characteristics and electrical characteristics and which can form a high resolution circuit pattern.
Intensive researches repeated by the present inventors in order to achieve the objects described above have resulted in finding that a novel polybenzoxazole precursor having a high purity can readily be produced at one step without producing any ionic by-products and therefore requiring a complicated refining step by reacting a bis-o-aminophenol compound with a dialdehyde compound, and they have come to complete the present invention.
Thus, the present invention provides a polybenzoxazole precursor having a repetitive unit represented by Formula (1): 
wherein A1 represents a tetravalent aromatic group; N and OH which are bonded to A1 are paired, and the respective pairs of N and OH are bonded to carbons which are adjacent to each other on the same aromatic ring; A2 represents a divalent organic group; and n represents a number of 2 to 300.
Further, the present invention provides a production process for the polybenzoxazole precursor having the repetitive unit represented by Formula (1) described above, characterized by reacting a bis-o-aminophenol compound represented by Formula (2): 
wherein A1 represents a tetravalent aromatic group; an NH2 group and an OH group which are bonded to A1 are paired, and the respective pairs of an NH2 group and an OH group are bonded to carbons which are adjacent to each other on the same aromatic ring with a dialdehyde compound represented by Formula (3): 
wherein A2 represents a divalent organic group.
Further, the present invention provides a coating composition comprising the polybenzoxazole precursor described above.
Still further, the present invention provides a positive type light-sensitive resin composition comprising the polybenzoxazole precursor described above and a light-sensitive quinonediazide compound.